Turcite vs Moglice vs Delrin

Hi,
I have been toying with the idea of making a 2 1/2D cnc router to cut out ribs
etc for model airplanes. My thoughts for the slides were hovering around
lengths of ground ms bar, the saddles being cut from box-section ms having holes

drilled for plastic bearing bushes. I've read around and am trying to determine
whether Turcite or Moglice or Delrin would be suitable for the bearing bushes ?
I have found Delrin readily on eBay but I know the other two materials are
specifically intended to be used in bearings, can anyone say which of these is
best in this kind of low load application, and whether the advantages outweigh
the convenience of Delrin ? Also a supplier of small quantities in diameters
between say an inch and half an inch would be helpful.
Many thanks,

Have you considered Glacier DU bushes? They're a steel/bronze/PTFE
composite, I haven't used any for donkey's years & don't know if it's
available now in standard sizes from the usual bearing houses but it
might be quite good for that sort of job?
Tim
Dutton Dry-Dock
Traditional & Modern canal craft repairs
Vintage diesel engine service

Excellent things DU bushes, every modern car would be
lost without them.
If you've got a car breaker local, bludge a couple of front
suspension struts off him. That will give you good lengths
of hard chrome bar and DU bushes, all good stuff for your
router table. As cars come in various sizes so do the struts.
Tom

I would seriously consider "ball bushing" bearings or whatever ball bearing
type linear slides are around on ebay etc, plain bushings of whatever type
are troublesome in the long run- I talk from industrial and home
experience-alternatively computer printers are a source of this type of
slide-good finish bar if bushes not salvageable, any independant computer
dealer will have loads, as will your local council tip-but that is a case of
dealing with jobsworths ( or bribes !)
Mark G.
wrote:

Er.. well yes my experience does include DU bushes from 8 mm to 50 mm bore,
they are good, but if you can get a ball bushing or other ball based linear
slide cheap you will be on a better route to success.-Does any decent
machine tool use otherwise ?
DU bushes are esentially a leaded bronze bush with a ptfe coating,steel
backed, great when new, but will not withstand well to intermitent side
loads such as in a machine slide.
Mark G.

They also can have some stiction compared to rolling element linear
bearings.
I used to use 1000's of 3/16" DU bushes on an instrument job I was
involved with. We found we had to burnish the bushes to stop it. The
shafts were mirror polished stainless steel.
My recommendation for CNC use especially when using stepper motors is
the lowest friction bearing you can find.
Wayne...

LOL Indeed. Do you think we didn't research the problem? This was a
very low force application <10g. Nevermind clever clogs you obviously
know more than the application engineers that helped us resolve it.
But back onto subject DU's have no real place in this application.

Obviously more than the designer who did the original specification.
I've been using or specifying either Glacier or INA bushings and wear
strips over 25 years, for units moving from 1 pound up to 10 tons,
without having to resort to "application" engineers to create a
workaround for a design fault.

Says you... Based on one experience. I suggest you acquaint yourself
with the INA Permaglide product application range.

You know I didn't notice you there 15 years ago when this happened,
maybe you were hiding in the closet. But I can assure you it was
designed to the glacier recommended parameters.
Tom each application has it's vices, what works well for one
application may not work so well for another. In this case the
instrument had very low internal force available to return the shaft to
it's zero position. In the end it was made to work and well. But not
quite so easily as Glacier said it would ;)
But it's History now, and I'm glad I've moved on.

No based on my cnc experience. No commercial machines that I know of
use DU's and rarely do they use round linear ways except on the cheapest
hobby machines. They just don't lend themselves to the rigidity required.
There are tons of surplus linear motion items available on ebay etc, and
the original poster might want to look to see whats available rather
than re-invent wheels.
I've seen lots of people get very annoyed and frustrated when their
homebrew cnc's don't perform well.
All my cnc milling machines use box ways, and bonded on Turcite as well
as automatic lube systems. I've used more modern machinery with bolt
on linear ways, and although nice and fast. SUCK for rigidity in many
cases.

Yes Tom I saw that. But having been around a lot of people doing
homebrew retrofits as has J.S. I have seen so many start off saying "I
only need this" But later wish they had made the machine to be capable
of doing "That" !
Same with the size issue!
Sadly reading through the posts on some of the CNC forums, there is
quite a lot of frustration. Most of which could of been avoided with a
little time spent earlier on planning the thing out.
Wayne..

http://web.onetel.com/~duttondock/Pictures/Ward-1.jpg
OK, I realise you probably meant current CNC machines, & this one is
neither current nor CNC. I just thought I would throw it in to be
mischievous. In fact it may well predate Turcite, Moglice etc., I
don't know when they became readily available?
Cheers
Tim
Dutton Dry-Dock
Traditional & Modern canal craft repairs
Vintage diesel engine service

Yes it is a controlled spiral cutter grinder, will grind spiral flutes
without the use of guide fingers as well as all the usual T&C
functions.
Made by Ward Grinders in Dorset, spiral grinders were their
speciality. No connection AFAIAA with the other lot.
Cheers
Tim
Dutton Dry-Dock
Traditional & Modern canal craft repairs
Vintage diesel engine service

Tim
I actually thought after I posted that maybe it was a product of Ward
Grinders in Parkstone, Poole. I have quite a few friends in the
business who served their time there. Maybe some of them worked on your
machine.
Long gone now I think.
Wayne...

Just to throw another oar in the water here.
I have had two personal experiences where the ball bushings were
replaced by the plastic lined bushings from RS and worked better.
Both were low force applications and both had problems with fine dust.
One was on the Y axis of a laser cutter and the fine dust and fumes
caused the ball bushing to tighten up in service.
Once on a service call we couldn't get any new bushings locally in
time and replaced them temporary with some RS lined bushes whilst
spares were ordered. They never got fitted as the lined bushes wiped
the shaft clean and it ran until it was scrapped a few years later.
Because of this experience I swapped the ball bushing on a CNC router
for lined bushings as the MDF dust was having the same problem and
again it cured the problem.
With better designed seals and covered bellows on the way the ball
bushings may have been no problem but with the skeletal build up of
both these machines the lined bushes cured what problems we had.
.
--
Regards,
John Stevenson
Nottingham, England.
Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk /

Yes a problem with round linear rod is that need to support it, and
therefore the slot required through the bearing to clear the supports.
It is one of the reasons I dislike them. The longer the travel you need
the worse the problem seems to get. As well as their need to be
elevated over any solid base.
Those NSk(etc) linear rails at least can be bolted down onto a flat
surface. I do realise there's a cost issue with those though ;) There
are bargains to be had if you look hard enough.
Wayne...

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